Methods and apparatus for cellular broadcasting and communication system

ABSTRACT

In a cellular wireless network, methods and apparatus are disclosed for a signal broadcasting scheme that can be individually augmented for users with poor reception. The network employs a first downlink channel for broadcasting data to all mobile stations, a second downlink channel for sending signals to a specific mobile station in a cell, and an uplink channel for feeding back information to the base station. To achieve a certain user reception quality, the system adjusts its broadcasting parameters based on the statistical analysis of the feedback data. If some users still require better reception, the system individually augments their broadcast signals via the second downlink channels. Methods and apparatus are also disclosed for synchronization of data distribution by base stations, which, in part, allows the receivers to combine the receiving signals and improve their reception quality.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. patent application Ser. No.11/571,468, having a 371 date of Nov. 28, 2007, which is a NationalPhase Application of PCT/US2006/011088, filed Mar. 24, 2006, whichclaims the benefit of U.S. Provisional Patent Applications No.60/665,184 and 60/665,205, filed on Mar. 25, 2005 by Waltical Solutions,Inc.

TECHNICAL FIELD

The disclosed embodiments relate, in general, to wireless communicationand include methods and apparatus for signal broadcasting which isaugmented by individual signals.

BACKGROUND

The evolution of wireless systems has followed two different paths:radio and television broadcasting. Wireless communication started withpaging and dispatch systems. Wireless voice communication became abooming industry in the past two decades. The last five years haswitnessed many wireless data communication systems such as wirelesslocal area network (WLAN) and broadband wireless access (BWA) systems.With digitalization and the advancements of the digital communicationtechnology, digital broadcasting has become a new trend with digitalvideo broadcast (DVB) and digital audio broadcast (DAB) systems asexamples.

Recently, there is a trend of merging wireless technologies to providesupport to multimedia applications in integrated environments. The thirdgeneration (3G) wireless communication systems have already integratedvoice and data services. The recent WiMax technology is focused on asingle platform to support broadband application with quality of service(QoS).

Naturally, the integration of the broadcast and the communicationsystems is the next step in the evolution of the wireless systems, butinvolves many challenges. For example, the broadcast system needs todeal with broadcast channels that have different characteristics. Also,the scheduler needs to optimally work with two downlink transmissionpaths: the broadcast channel and the regular (individual) channel.However, integration of a broadcast system with a communication systemwithout sharing certain control information is not an optimizedsolution.

In a broadcasting system, content data from the source is delivered tomultiple transmission base stations, which broadcast to receivers usinga particular transmission method such as Orthogonal Frequency DivisionModulation (OFDM). To alleviate the problem of interference fromdifferent base stations, the broadcasting data is simultaneouslytransmitted by all the base stations using same time/frequency resource.This type of network configuration is commonly known as the singlefrequency network (SFN), which has been used in applications such as thedigital video broadcasting (DVB) system.

In the case of the DVB, the broadcasting video data, which is in theformat of Moving Picture Experts Group 2 (MPEG-2) transport streams, iscoded into a mega-frame format and is distributed to the base stationswith a time stamp in the synchronized bit stream. The base stations areall synchronized to a common time source and use the time stamp tosynchronize exact transmission time of the broadcast data. However,recently more and more new wireless data network infrastructures usepacket data networks as their backbone. A packet data network has abursty packet arrival pattern, random receiving packet order andmultiple distribution paths, which is significantly different from thoseof the MPEG-2 transport streams. Therefore, the DVB approach is notsuitable for a packet data network and for a SFN video broadcasting thatuses a packet data network backbone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates system architecture of a cellular wireless system.

FIG. 2 illustrates a cellular system with a base station that broadcastsdata to mobile stations using either a downlink broadcast channel or adownlink regular channel.

FIG. 3 illustrates an adaptable frame structure (AFS) in a TDD system,wherein each subframe in a TDD frame can be designed to fit a specialapplication.

FIG. 4 illustrates two examples of channel scheduling for an AFS system,using multiple frequency bands.

FIG. 5 illustrates another example of a system frame structureconfiguration that has two types of 5 ms frames: a video frame and adata frame.

FIG. 6 illustrates system architecture of an Intelligent SchedulingAgent (IMA).

FIG. 7 illustrates an example of an intelligent bit stream schedulingfor AFS.

FIG. 8 illustrates a basic architecture of a synchronized packetdistribution network (SPDN).

FIG. 9 is an example of a distribution data packet format.

FIG. 10 is another example of the distribution data packet format.

FIG. 11 is yet another example of the distribution data packet format.

FIG. 12 illustrates a distribution data packet format.

FIG. 13 illustrates DA and RA processes.

DETAILED DESCRIPTION

Various embodiments of the invention will now be described. Thefollowing description provides specific details for a thoroughunderstanding and enabling description of these embodiments. One skilledin the art will understand, however, that the invention may be practicedwithout many of these details. Additionally, some well-known structuresor functions may not be shown or described in detail, so as to avoidunnecessarily obscuring the relevant description of the variousembodiments

The terminology used in the description presented below is intended tobe interpreted in its broadest reasonable manner, even though it isbeing used in conjunction with a detailed description of certainspecific embodiments of the invention. Certain terms may even beemphasized below; however, any terminology intended to be interpreted inany restricted manner will be overtly and specifically defined as suchin this Detailed Description section.

The disclosed embodiments of this invention present methods andapparatus for cellular broadcasting and communication systems. Themultiple access technology mentioned herein can be of any special formatsuch as Code Division Multiple Access (CDMA), Time Division MultipleAccess (TDMA), Frequency Division Multiple Access (FDMA), OrthogonalFrequency Division Multiple Access (OFDMA), or Multi-Carrier CodeDivision Multiple Access (MC-CDMA).

Without loss of generality, OFDMA is employed herein as an example toillustrate different aspects of these embodiments. The cellularbroadcasting and communication system can operate with both the timedivision duplexing (TDD) and frequency division duplexing (FDD).

In a wireless network, there are a number of base stations, each ofwhich provides coverage to its designated area, normally called a cell.If a cell is divided in to sectors, from system engineering point ofview each sector can be considered as a cell. In this context, the terms“cell” and “sector” are interchangeable.

A base station serves as a focal point for distributing information toand collecting information from its mobile stations by radio signals.The mobile station is the communication interface between the user andthe wireless network. The transmission from a base station to a mobilestation is called a “downlink” and the transmission from a mobilestation to a base station is called an “uplink.” The terms “user” and“receiver” have been used interchangeably. The term “mobile station”represents the user terminal in a fixed wireless system or a portabledevice with the wireless communication interface. FIG. 1 shows thesystem architecture of a cellular system.

There is at least one control server (CS) in a multi-cell wirelessnetwork, which controls one or multiple base stations (BS). The controlserver is connected to the base stations via the backbone network. Thebackbone network can be either wired network or wireless network. It canalso be either a circuit switched network or a packet data network. Thebackbone network may also connect to other servers in the system, suchas a number of authentication/authorization/accounting (AAA) servers,content servers, and network management servers.

A “Cellular Broadcasting and Communication System” is a special type ofcellular wireless system. In the following description, the term“Cellular System” is used as an abbreviation of the “CellularBroadcasting and Communication System.” The Cellular System employs atleast three radio channels, as described below:

-   -   1. Downlink Broadcast Channel, which carries the broadcast data        signal to all the mobile stations. For each cell, the broadcast        signal can be transmitted independently or in a coordinated        manner, using technologies such as SFN (same frequency network).    -   2. Downlink Regular Channel, which carries the signal designated        to a specific mobile station in a cell. Antenna beam forming and        multicast technologies can be used to enhance the transmission        on downlink regular channels.    -   3. Uplink Channel, which can be used to send feedback        information that may include receiver requests, the ACK/NACK for        each downlink data packet, and/or the downlink signal quality        information of each individual mobile station.

In many multimedia applications, the application data is encoded intomultiple application bit streams by the content server, using sourcecoding schemes. The disclosed embodiments also define a system componentcalled IMA (Intelligent Scheduling Agent) in the transmitter of a basestation, which maps multiple application streams into the underlyingwireless channels based on the system control information and thefeedback from the receivers.

The base station transmits broadcasting data to mobile stations via thedownlink broadcast channel or the downlink regular channel. The choiceof scheduling method for a particular bit stream and for a specificradio channel directly impacts the system behavior, such as the systemcapacity and performance. This is because the two types of downlinkchannels have different characteristics. Special arrangements can bemade for a group of individual mobile stations to improve the overallcoverage. Furthermore, based on the feedback information transmitted byindividual mobile stations through the uplink channel, augment signalscan be sent to selected individual mobile stations if their receivedsignals need improvement.

Cellular Broadcasting and Communication System

For each cell, the (downlink) broadcast signal can be transmittedindependently or in coordination. In one embodiment, multiple basestations are coordinated to transmit the same broadcast signalsimultaneously using single frequency network (SFN) technology. Themodulation and coding scheme (MCS) of the downlink broadcast channel isusually affected by general statistics of the wireless system, possiblyobtained through pre-deployment site survey or cellular networkplanning.

The downlink regular channel, which is usually defined for a singlecell, carries signals that are designated to one mobile station.Typically, for each mobile station the regular channel signal contentand/or format is different. The data content also includes downlink dataand control information such as digital rights management messages. TheMCS of the downlink regular channel is determined by individual user'sdownlink signal quality, which is obtained from the user feedback.Antenna beam forming can enhance the signal quality of the downlinkregular channel. Data transmission to multiple mobile stations in thedownlink regular channel may also be combined to use multicast schemes.

The mobile stations use the uplink channel to transmit uplink data tothe base station, which includes both data and control information suchas digital rights management messages. The uplink channel can also beused to send feedback information that may include:

-   -   1. Receiver Request, wherein a receiver can specify its        preference, or request something via the uplink channel. The        request, for example, can be a command entered by a user to        switch to another TV program or to order a high definition TV        program.    -   2. A Receiver Feedback, wherein the feedback may indicate        downlink channel receiving quality. In one embodiment, the        Signal to Noise Ratio (SNR) of the downlink channel is reported        in the uplink channel. The receiver feedback information may be        packet based, such as automatic repeat request (ARQ) feedback.

In a Cellular System, as illustrated in FIG. 2, the base stationtransmits broadcasting data to mobile stations through either thedownlink broadcast channel or the downlink regular channel. The systemaugments the broadcast signals to those individual users that feed backan unacceptable quality of downlink signals. The system augments areprepared based on the feedback information transmitted by the individualmobile station through the uplink channel.

The following embodiments are examples of Cellular Systems usingdifferent frame structure and transmission schemes.

In some embodiments an adaptable frame structure (AFS) system isemployed wherein a transmission frame comprises multiple subframes, eachcontaining a downlink transmission period and an uplink transmissionperiod. A downlink broadcasting signal is used to indicate to thereceivers the configuration of each subframe.

The downlink and uplink period configuration in each subframe can beindependently adapted to support applications with a variety of trafficpatterns, from symmetric to highly asymmetric. A frame is divided intomultiple subframes with flexible mix of subframe types. Therefore, agreat variety of applications such as normal two-way datacommunications, voice communications, video, and data broadcasting areefficiently supported in a single frequency band. Using multiplefrequency bands increases capacity or adds more flexibility. As shown inthe embodiment of FIG. 3, each subframe in a TDD frame is designed tofit a special application, such as voice, data, or video.

In one embodiment, a cellular system uses AFS, the frame of which hastwo different types of subframes: the video and the data subframes. Thevideo subframe is used as the downlink broadcast channel. The datasubframe includes a downlink period that is used as downlink regularchannel, and an uplink period that is used for transmitting uplinkfeedback information.

In another embodiment, the video subframe of the AFS system uses SFN tosimultaneously broadcast the same radio signal from the base stations.

In yet another embodiment, there are multiple frequency bands in an AFSCellular System. Without loss of generality, FIG. 4 shows a system withtwo frequency bands f₁ and f₂. Based on the system configuration, theAFS video and data subframes can use both bands. In one embodiment eachfrequency band is used by the two downlink and the one uplink channelsand in another embodiment one frequency band is exclusively used by thedownlink broadcast channel and the other is used by the downlink regularchannel and the uplink channel. The downlink broadcast channel isdefined as the video subframe in both frequency bands.

With a more generic definition for adaptive frame structure, a CellularSystem can have two types of 5 ms frames: the video frame and the dataframe. As shown in FIG. 5, these two types of frames are interleaved.The mixing ratio of the frame types is defined either by the systemconfiguration or by the incoming data pattern. The uplink period of adata frame is used as the uplink channel, the downlink period of thedata frame is used as the downlink regular channel, and the video frameis used as the downlink broadcast channel.

Frame configuration 4 in FIG. 5 illustrates a special design to reducepower consumption of those mobile terminals which only receive videobroadcast data. The mobile terminal only wakes up periodically at thevideo frame when its video burst is broadcasted. It buffers the videocontent up to its burst buffer limit and goes into power saving modeafterwards. With the buffered video data, it can play back video streamcontinuously. The mobile terminal remains in the power saving mode untilthe next video burst arrives.

Multiple Application Bit Streams

In many multimedia applications, using a source coding scheme, theapplication data is encoded by the content server into multipleapplication bit streams. In the presented embodiments, these streams areidentified by S1, S2, . . . , Sn, where n≧1.

In one embodiment, a digital TV program is encoded and compressed intothree bit streams; namely, an audio stream, a basic video streamcontaining low resolution video information, and a complementary videostream that carries differential information for a receiver toreproduce, together with the basic bit stream, high-resolution images ofthe same video content.

In another embodiment, the broadcast data is encoded into two bitstreams for reliable transmission. The original bit stream isbroadcasted in sequence. If a receiver fails to receive the originaldata, it can request retransmission bit stream which contains those lostpackets.

In yet another embodiment, high definition television (HDTV) broadcastdata is encoded into three streams using hierarchical source code. S1contains a basic video stream for low resolution receivers in mobiledevices such as cell phones and personal data assistants (PDA). S2 is acomplementary video stream that carries the differential information fora receiver to replay the same program with standard definitiontelevision (SDTV) quality. And S3 carries the differentiationinformation between SDTV and HDTV.

The bit streams generated by the content server may be forwarded to thebase-stations directly or relayed to the base stations via their controlserver. The bit streams may also be modified by the control server toadd control information. The control information will be removed whentransmitted from the base stations to the mobile stations.

In one embodiment for SFN based broadcast, the original streams S1, S2,. . . , Sn, are first transmitted to the control servers. The controlservers insert time synchronization information tags and attach them tothe streams. The modified streams S1′, S2′, . . . , Sn′ are transmittedto the base stations via the backbone network. The base stations use thetag to synchronize their transmission time. The attached tags areremoved from the streams when they are broadcasted to the mobilestations.

Intelligent Scheduling Agent

The multiple bit streams are mapped into the underlying two downlink,radio channels in a Cellular System by a system component called an“Intelligent Scheduling Agent” (IMA). FIG. 6 illustrates the systemarchitecture of an IMA. In one embodiment, there are five systemcomponents in an IMA: (1) Transmission Mapping Engine, (2) ApplicationBit Stream Queues, (3) Scheduler, (4) Decision Making Database, and (5)Feedback Collector. The IMA components can be implemented as distributedsoftware processes. In a Cellular System, the IMA system components caneither reside in the control server or be integrated with the basestation.

The input application bit streams are first stored in the ApplicationBit Stream Queues. A scheduling data or decision is made by theScheduler, which consults with the Decision Making Database for systemcontrol information, and generates scheduling decisions based on systemobjectives. The Transmission Mapping Engine multiplexes the bit streamsinto different channels based on the scheduling decisions. The FeedbackCollector forwards receiver feedback to the Decision Making Database,which will be used by a scheduling algorithm of the Scheduler.

In one embodiment, the Application Bit Stream Queues, Scheduler, andDecision Making Database are implemented in the control server and theTransmission Mapping Engine and the Feedback Collector are implementedin the base station. The scheduling decision is forwarded to theTransmission Mapping Engine together with the application data stream.The Feedback Collector reports the user feedback information back to thecentral control server, where the Decision Making Database is updated.

In another embodiment, all the IMA system components are integrated withthe base station in an AFS Cellular System. As illustrated in FIGS. 7,S1, S2 and S3 are generated by the content server and transmitted to thecontrol servers first. The control servers insert time synchronizationtags into the streams and then forward them to the base stations via thebackbone network. The time synchronization tags are used to indicatetransmission time for all the base stations in SFN operation. Themodified S1, S2 and S3 streams are marked as S1′, S2′, and S3′.

The adaptable frame structure has a video subframe which performs 16QAMwith SFN. The tags in the streams are removed by the base stations andthe original S1, S2 and S3 are broadcasted simultaneously. The IMA ineach base station buffers the S1 in its application bit stream queue.For a user who cannot decode the video subframe correctly, the basestation will establish a downlink regular channel to the user based onthe user's request and a channel quality report. The regular channel isdefined in the AFS data subframe using QPSK modulation.

Application Bit Stream Queues

The application bit streams generated by the content server are firststored in the queues of the IMA. However, queuing may not be necessaryfor some applications. In one embodiment, the video broadcastapplication bit stream is mapped into broadcast channel directly. Inanother embodiment, the application bit stream remains in the queue forreliable data transmission until acknowledgements from all receiverscome back.

Feedback Collector

In a wireless system with a feedback channel on the reverse linkdirection, the Feedback Collector collects all the feedback informationand relays them to the Decision Making Database. Feedback information ispart of the control information the Scheduler will use to make optimalscheduling decisions.

Decision Making Database

A scheduling decision is made by the IMA agent based on the informationfrom the Decision Making Database and the scheduling algorithm. Theinformation stored in the Decision Making Database include:

-   -   1. Application Information: An application may have its own        distinctive requirements and preferences regarding channel        scheduling decisions. In one embodiment, the original bit stream        of a reliable broadcast data application is transmitted via the        downlink broadcast channel with the retransmission stream        scheduled into the regular channel.    -   2. Wireless Channel Information: The wireless channel        information is important to the decision making process. The IMA        needs to be aware of the wireless channel characteristics such        as the signal quality, frequency, latency, etc.    -   3. Feedback Information: System augments can be based on the        feedback information transmitted by the individual mobile        station in its uplink channel. Examples are the receiver        request, the ACK/NACK for each downlink data packet, and/or the        downlink signal quality information.    -   4. Network Management Information: The network management system        may impose an administration rule on the scheduling decision. In        one embodiment, the users are classified by their terminal        devices. Those using cell phones and PDAs can only receive low        resolution basic video stream. While others using fixed        terminals can additionally receive the complementary video        stream to play back high resolution video. In another        embodiment, the users are configured by their subscription        types. The basic video stream is broadcasted via the downlink        broadcast channel to mobile TV subscribers. SFN may be used in        the downlink broadcast channel. The complementary video stream        is transmitted in the downlink regular channel to those        subscribed for high resolution TVs. Beam forming may be used to        enhance the receiving quality for the HDTV subscribers.

In accordance with the embodiments of this invention, the IMA, eitherjointly or individually, applies relevant tables in the database to makescheduling decisions.

Since the environment of the system is changing, the information storedin the Decision Making Database is updated, sometimes frequently, toreflect the changes. Some information is derived locally from othersystems. In one embodiment, when an application stops, the applicationinformation table is updated. Some information, such as the channelquality feedback and the receiver request, is fed back from thereceivers through the uplink channel.

Scheduler

The Scheduler tries to make optimal scheduling decisions to achievecertain system objectives. It consults the Decision Making Database anduses its data as the input to the scheduling algorithm. First, thescheduler decides if the broadcast channel and the regular channelshould be used for the data transmission. If both channels are used, theincoming data is dispatched into different channel message queues. Thenthe scheduler determines the MCS and transmission technologies used forthe channels and allocates the air link resource to both channels.Finally, the data is mapped into the underlying physical channels andtransmitted to the mobile stations after the physical layer finishescoding and modulation.

Transmission Mapping Engine

The scheduling decisions are forwarded to the Transmission MappingEngine, which is in charge of retrieving the application bit stream andputting it into the correspondent wireless channel.

Methods for Cellular Broadcasting and Communication System

The mobile terminals measure the downlink signal quality for both thedownlink broadcast channel and the downlink regular channel.

In one embodiment, in an AFS Cellular System, the broadcast channel andthe regular channel occupy different subframes. Their signal quality canbe measured in a time sharing fashion by the mobile terminal using thesame radio frequency (RF) receiver circuitry.

In another embodiment, in a multiple frequency band AFS System, usingsubframe configuration 1 shown in FIG. 4, the broadcast channel and theregular channel are separated by different transmission times. Themobile terminal can still use the same RF receiver circuitry to measurethe signal quality using time sharing.

In yet another embodiment wherein configuration 2 of FIG. 4 is used in amultiple frequency band AFS Cellular System, the broadcast channel andthe regular channel are both used to transmit data at the same time. Inthis case, the mobile terminal uses two RF receiver circuitries tomeasure the signal.

The base station allocates the uplink channel resource to the mobileterminals, such as time/symbol and frequency/subchannel, for sending themeasurement reports.

In one embodiment, the base station defines channel quality index (CQI)feedback regions for both the downlink broadcast channel and thedownlink regular channel. The AFS CQI feedback regions are specified inthe uplink channel by their subframe number, symbol index range, andsubchannel index range.

By using the uplink channel, the base station can collect both thedownlink broadcast channel and the downlink regular channel qualityinformation from the mobile stations. The quality report can be updatedby the mobile stations periodically. The mobile stations can also bepolled by the base station or be triggered to send their reports by apredefined system event or threshold.

In one embodiment, with the real-time channel quality information, theMCS of the downlink broadcast channel is updated accordingly, which canoverride the default MCS derived from the pre-deployment site surveyresult.

The two types of downlink channels in the Cellular System have differentcharacteristics. The MCS of the downlink regular channel is selected bythe Medium Access Control (MAC) based on the received signal quality ofthe individual user. Most of the time the MCS of the broadcast channelis determined by general statistics of the wireless system, possiblyobtained through pre-deployment site survey or cellular networkplanning.

When SFN is used, the broadcast channels of the neighboring basestations are coordinated to transmit simultaneously. However, theregular channel is always defined in a single cell. Additionally,advanced antenna transmission technology, such as beam forming, can beutilized in a regular channel to improve the SNR for a particular user.

Because of the differences of the channel characteristics, the choice ofthe scheduling method for a particular bit stream and for a specificradio channel will directly impact the system behavior, such as thesystem capacity. For example, the system bandwidth to transmit the sameN bits of data to M users using the regular channel with 16QAM is N*M/4Hz. However, using QPSK in the downlink broadcast channel will take thesystem bandwidth up to N/2 Hz. Therefore, the broadcast channel is morebandwidth efficient if M>2.

Special arrangements can be made for selected individual mobile stationsto improve the overall coverage. In one embodiment, the mobile stationcaches the broadcast data from the content server in the downlinkbroadcast channel. When it detects a missing packet, it will send to thebase station a NACK control message via the uplink channel. The basestation then retransmits the missing packet via the regular channelusing the MCS according to the fed back downlink signal quality of themobile station.

System augments can also be made based on the feedback informationtransmitted by the individual mobile stations in their uplink channel.In another embodiment, a mobile station reports the downlink signalquality to the base station. The base station may determine that thereported SNR is insufficient for this particular mobile station wheneverdata is broadcasted via the downlink broadcast channel in the SFN. Insuch a case, the base station will adjust MCS, the MAC resourceallocation (time, frequency, subchannels), and power, etc. to send thesignal to the mobile station in the regular channel. The base stationcan also use beam forming to improve the downlink signal quality for theuser. The transmission parameters are specifically selected for thatuser, based on the feedback.

In yet another embodiment, the SFN enabled broadcast channel is used totransmit SDTV program (S1+S2) using hierarchy modulation scheme. If auser experiences difficulties decoding S1 from the broadcast channel, itsends a feedback signal via the uplink regular channel. The feedbackcontains the channel quality report and the user request. Upon receivingthe feedback report, the serving base station starts to forward S1 tothe user through a downlink regular channel, with or without beamforming. In another embodiment, if a user wishes to receive an HDTVsignal, it sends a request along with a feedback report with the channelsignal quality to the serving base station. A downlink regular channelis used to transmit S3 to the user after the base station validates therequest.

Hierarchy modulation may also be used to transmit bit streams in awireless communication system. Table 1 illustrates an example of thescheduling between the hierarchical bit streams and its correspondentmodulation schemes for HDTV broadcast using multiple bit streams.

TABLE 1 Scheduling between hierarchy modulation schemes and multipleapplication bit streams Hierarchy Modulation Schemes MultipleApplication Bit Streams 64QAM HDTV quality broadcast (S1 + S2 + S3)16QAM SDTV (S1 + S2) QPSK Mobile TV (S1)

Methods and apparatus are also provided for synchronized datadistribution in a packet data network. Simultaneous broadcasting of thesame content by the base stations, using the same time/frequencyresource, allows the receivers to combine the received signals fromdifferent base stations and improve their reception quality. Asmentioned above, in each multi-cell wireless deployment, there is atleast one control server (CS) that controls one or multiple basestations (BS). The control server is connected to the base stations viathe backbone network. In the presented embodiments, the backbone networkis a packet data network that can either be a wired or a wirelessnetwork. Without loss of generality, IPv4 is used to illustrate theseembodiments.

The wireless system described herein is associated with a certaintransmission format. The frame duration and its structure can bedescribed by a mathematical function of time. All the base stations arealigned in transmission time at the frame boundary. The sequence of theframe and its relationship to the time is known to all the BSs and CSs.

FIG. 8 illustrates a basic architecture of a synchronized packetdistribution network (SPDN). The SPDN has a Distribution Adapter (DA)which receives original application data packets and, after adding theadditional protocol information, distributes them across the packetdistribution network (PDN) to the base stations. The additional protocolinformation added by the DA includes time synchronization information,resource scheduling information, and protocol control information. Theinputs to the DA are original data packets, whereas the outputs from theDA are distribution data packets.

In each base station, a device called the Receiving Adapter (RA) ensuressimultaneous data transmission among the base stations by using the samedata content and the same time/frequency resource. The RA will retrievethe time synchronization information in the distribution data packet anduse it to control the start time of data transmission. All the packetswill be buffered and sorted to re-establish the delivery sequence beforethey are broadcasted over the air. A synchronization distributionprotocol is defined for the SPDN. Both the RA and the DA may synchronizewith the same time reference, such as the global position system (GPS)signals.

The SPDN distribution network protocol is carried out on top of theunderlying data network protocol. The distribution network protocol istransparent to the underlying data network devices. Segmentation andreassembly may be necessary at the DA and the RA at each base station.

SFN in Cellular Broadcasting and Communication System

In wireless applications such as digital video broadcasting, SFNtechnology is used to alleviate the problem of interference between basestations. Even if OFDM is used in the system, simultaneous transmissionof the same broadcasting content by the base stations, using the sametime/frequency resource, allows a receiver to combine the receivingsignals from different base stations and boost its SNR. The underlyingwireless system is associated with a certain transmission format. Allthe base stations are aligned in transmission time at the frameboundary. The sequence of the frame is known to all the BSs and CSs viaa synchronization distribution mechanism.

In one embodiment, the base stations are synchronized with each otherfor transmission. Furthermore, the system frame structure is defined bya distributed frame number synchronization mechanism while a commonframe number scheme is shared between the CS and BSs. The common framenumber is increased every frame by both the CS and the BSs. Thedistributed frame number synchronization mechanism makes sure the framenumber is always in sync within the network.

The same mechanism can be used to derive common super-frame and subframenumbers as long as the frame structure is predefined in the system withsome mathematical relationship between the numbers. For example, if eachframe has 4 subframes, the subframe number can be expressed by 4N+M,where N is the common frame number and M is the sequence number of asubframe within the frame.

In another embodiment when adaptable frame structure (AFS) is used in aTDD wireless system, each TDD frame has multiple subframes. Eachsubframe, as shown in FIG. 3, can be designed to fit a specialapplication, such as voice, data, or video. A frame is divided intomultiple subframes with flexible mix of subframe types. The framestructure is known to both CS and BSs, and all the BSs are synchronizedand align their transmission along the subframe boundary. A commonsubframe number scheme is maintained in the system. Furthermore, the CSknows the exact video subframe capacity derived from the predefinedcoding/modulation scheme for the video subframe. The video payloadlength of each video subframe can be calculated by subtracting theoverhead bits from the overall subframe capacity.

The CS and the BSs are connected by a packet data network (PDN). The PDNis designed with the maximum PDN transmission delay known to both CS andBS. In a packet data network, information is transmitted in a datapacket with source and destination addresses in the header. Thedisclosed embodiments do not impose any restriction on the networkprotocol or transmission technologies used in the packet data networks,such as Ethernet, Internet Protocol version 4 (IPv4), IPv6, ATM.Therefore, without loss of generality, IPv4 is employed herein toillustrate the operations of these embodiments.

The SPDN, with its two system components DA and RA, is built on top ofthe underlying packet data network that connects the CS and the BSs. DAis located in the network and is in charge of producing the distributionnetwork packets with additional protocol control information. RA islocated in the base station. It first retrieves the time synchronizationinformation from the distribution data packet and then delivers theoriginal data to the BS at the exact frame based on the timesynchronization information.

The distribution data packets must arrive at the RA before thetransmission start time specified in the packet. The DA has to take intoaccount the maximum PDN transmission delay when calculating the timecontrol information for the distribution data packet. Distribution datapackets are buffered at the RA before they are sent to the BS forbroadcasting at the exact time.

SPDN Architecture

The architecture of the SPDN and the description of some of itscomponents are presented below. While specific embodiments and examplesare hereby described for illustrative purposes, various equivalentmodifications are possible within the scope of the invention. Someaspects of these embodiments can be applied to other systems. Also, theelements and acts of the various embodiments described here can becombined to provide further embodiments.

Distribution Adapter

The DA receives original data packets and distributes them across SPDNto the RAs in the base stations. Distribution takes place after addingthe supplementary protocol information using the synchronizationdistribution protocol. Therefore, the input to the DA is the originaldata packets and the output to the DA is the distribution data packets.

The DA may distribute original data packets from multiple applicationdata sources. For example, in IPTV applications, each TV channel is anapplication data source that generates its own data packets. Hence, theDA may need to be aware of the application data source.

On the other hand, the SPDN may have multiple DAs; each of them takingcare of the original data packets from one or multiple application datasources. In such a case, the DAs may need to coordinate with each other.The typical protocol information added by the DA can include:

-   -   1. Time synchronization information, wherein DA determines the        start time of the data transmission for the base stations. Such        start time is part of the time synchronization information. The        maximum PDN transmission delay also needs to be considered.        Since the data and the time information has to arrive at the RA        in advance, the start time must refer to some future time value        that is greater than the maximum PDN transmission delay. For        example, if the maximum PDN transmission delay is 500 ms, the        start time of data transmission has to be a time sufficiently        longer than 500 ms, such that when the start time is received        and decoded at the RA, it still refers to a time in the future        for transmission. If it indicates a time that has already        passed, the base station RA shall disregard the data and may        generate an error report. In one embodiment for AFS system, the        time synchronization information is expressed by the video        subframe number. The DA notifies the RA of the exact video        subframe for video broadcasting, using the associated        distribution data packets.    -   2. Resource scheduling information, wherein the DA may also        determine what air link resource should be used for the data        transmission, in which case the Medium Access Control (MAC)        scheduling function is carried out by the DA. In one embodiment,        the AFS subframe number is used as an indicator of the air link        resource. Given a particular video data packet, the DA specifies        the video subframe number for it to be transmitted by all the        base stations. In another embodiment, the DA assembles video        data packets into one distribution data packet, which fits into        an AFS video subframe. Then the new distribution data packet is        sent to the base stations with the corresponding video subframe        number as transmission time reference.    -   3. Application specific control information, where in addition        to the air link resource scheduling information, the DA may also        include other application specific control information that        helps improve system performance. For example, power saving is        critical for battery operated terminals in the system. If there        is no data to receive, a terminal will stay in the power saving        mode and wakes up periodically to check for the new data. If        there is no pending data, the terminal goes back to the power        saving mode. In one embodiment, the DA does the resource        allocation and also announces the next scheduled SFN        transmission time. The terminal in the power saving mode only        wakes up in time before the scheduled video subframe and starts        receiving its data. It reduces the unnecessary wake up times and        therefore further reduces the power consumption. In another        embodiment where BS is in control of the MAC scheduling, it        broadcasts the transmission prediction information within the        cell.    -   4. Protocol control information, wherein the packet delivery        sequential order may be lost in the data network. To make sure        every base station transmits the data in a correct sequential        order, some protocol control information such as the packet        sequence number is needed.

The SPDN protocol guarantees the in-order distribution data packetdelivery. SPDN may also verify the distribution data packet integrity byadding redundant error detection protocol control information. In oneembodiment, a new cyclic redundancy check (CRC) is added to thedistribution data packet. In another embodiment, the error detectioncode of the original data packet is recalculated to protect the wholenew distribution data packet.

The DA can insert the additional protocol information in the beginning,in the middle, or at the end of the original data packet.Packet-specific information, such as the packet sequence and timesynchronization information, is inserted into every data packet. Theinformation common to multiple packets, such as the resource indicationfor several data packets, is only inserted once every N packet, where Nis greater than or equal to one.

Distribution Network Protocol

The distribution network protocol defines rules for distribution datapackets delivery to the base stations. The protocol is built on top ofthe underlying data network protocol. Without loss of generality, IPv4is used to illustrate the design of the distribution network protocol.

Distribution Data Packet Format

A distribution data packet is formed by inserting theadditional/supplementary protocol information to an original datapacket. The additional protocol information is inserted in thebeginning, in the middle, or at the end of the original data packet.Without loss of generality, in some embodiments, the distributionprotocol header contains all the additional protocol information. It mayalso contain the source and destination addresses of the distributionprotocol.

In one embodiment, the distribution protocol header is inserted betweenthe original data packet header and the original data packet payload. Inthis embodiment, the source and destination addresses of the originaldata packet remain unchanged and the SPDN relies on the underlyingrouting protocol to distribute the distribution data packet. Theoriginal data packet checksum is recalculated to reflect the change ofpacket payload. FIG. 9 shows the format of a distribution data packet.

In another embodiment, encapsulation is used to generate thedistribution data packet. A new distribution protocol header is added atthe beginning of the original data packet. The header contains theadditional protocol information for the base station RA to recover timesynchronization information, such as the frame number index for databroadcasting by all the base stations. A CRC is also appended at the endof the distribution packet, as illustrated in FIG. 10.

FIG. 10 also illustrates another embodiment of distribution data packetformat. In order to reduce the encapsulation overhead, the DA uses aheader compression algorithm for the original data packet. At the RA,the original data packet will be restored by taking out the distributionprotocol header and decompressing the original data packet header.

In yet another embodiment, the DA, based on the knowledge of the exactair-link resources for data broadcasting, assembles multiple originaldata packets together in the new distribution data packet. Thedistribution data packet payload fits in the broadcasting air linkresources. A new protocol header is constructed to carry the additionalprotocol information together with the source and destination addresses.The new CRC is also generated and appended, as shown in FIG. 11. Oncethe RA receives the distribution data packet, it forwards the payload tothe base station at the time indicated by the time synchronizationinformation in the distribution protocol header.

In another embodiment, the DA segments the original data packet intoseveral pieces and transmits them across PDN with the distributionprotocol header. At the base station RA, they will be reassembledtogether. FIG. 12 shows the format of such a distribution data packet.

Packet Transmission

The distribution network protocol is implemented on top of theunderlying data network protocol. The protocol runs between the DA andthe RA in the base stations. Only the end systems, namely the DA and theRA, are aware of the protocol. It is transparent to the underlying datanetwork devices, such as routers in an IP data network.

The packet transmission is based on the multicast technology. If theunderlying network architecture does not support multicast, such as PPP(point to point protocol), the multicasting function is simulated bytransmission of duplicated distribution packets over multiple unicastnetwork links.

In one embodiment, the DA segments the original data packet to fit intothe maximum transfer unit (MTU) of the underlying data network protocoland the RA reassembles the original data packet from its fragments.

The distribution network protocol may also try to achieve reliable datatransmission on top of the underlying network protocol, implying that aretransmission based on the acknowledgement may be necessary. In anotherembodiment, the reliable multicast techniques are used in thedistribution network protocol. For example, the RA reports to the DAabout any packet loss, based on the protocol control information such aschecksum and sequence number. The DA will then retransmit the requesteddistribution packet.

Receiving Adapter

The RA in a base station ensures that the synchronized data transmissionamong all base stations carries the same data content, with the sametime/frequency resource, and at the same time. When a distribution datapacket arrives at the base station, the RA will retrieve the necessaryinformation needed for transmission over the air link. Since theunderlying packet data network may alter the packet arrival order, theRA needs to buffer the distribution data packets and restore thedelivery sequential order based on the protocol control information inthe distribution protocol header. It may also reassemble the originaldata packets if segmentation is performed at the DA. Similarly, whenheader compression is performed at the DA to the original data packetheader, the RA is responsible for restoring the original packet headerby decompression.

In case the RA is not able to recover all the distribution packets dueto errors, it activates the error protection mechanism to avoid theinterference with the transmission by base stations. For example, a basestation must not transmit a distribution data packet if its transmissiontime has already passed when it arrives at the base station. Instead,the base station discards the overdue packet and remains silent for theduration of the transmission period for the overdue packet.

Design Illustration

In this section, an illustration is provided to understand the design ofSPDN. Without loss of generosity an AFS TDD wireless system is employed.The multi-cell deployment has one CS and multiple BSs. They areconnected with IPv4 packet data network with the assumed maximum PDNtransmission delay of 500 ms. IP multicast is supported for datatransmission between CS and BSs. All the BSs are aligned in theirtransmission time at the TDD frame boundary. The frame duration is 10-mslong and each frame consists of 4 subframes. The subframe duration is2.5 ms. A synchronization mechanism for the distributed frame number isin place so that the CS and BSs share a common frame number and, basedon it, a common subframe number is derived. Based on the video subframeduration, the usable data bandwidth of the subframe, and the predefinedcoding/modulation scheme (QPSK with ½ rate coding) the CS calculatesthat N bytes of data can be transmitted in a video subframe.

In one embodiment, the DA, with the knowledge of the video subframecapacity of N bytes, assembles the incoming video packets into adistribution data packet with data payload length of N. When the RAreceives such a distribution data packet, forwards its data payload tothe physical layer directly at the broadcasting subframe, which shouldfit exactly into the resource after coding and modulation. Thedistribution data packet header contains the starting subframe numberfor the SFN broadcast, which is generated base on the common subframenumber scheme.

Since the maximum PDN transmission delay is 500 ms or equivalently200-subframe long, the starting subframe number will not exceed 256 in amodular operation. Therefore, only 8 bits are needed to identify thestarting subframe number within the SPDN. For example, when the currentcommon subframe number is 0, the DA sends out a distribution packet andassigns to it the starting subframe number of 200. When the RA receivesthe distribution packet, because of the PDN transmission delay (e.g.,495 ms), the common subframe number has advanced from 0 to 198. The RAwaits for 2 subframes so that the common subframe number is equal to thespecified value 200 and forwards the data packet to the BS fortransmission.

The subframe number is based on a modular 256 calculation in theexample. If the distribution data packet length is larger than the MTUof the PDN, the DA further segments the packet into several transmissionpackets. The distribution data packet header contains an 8 bits commonsubframe index. In this case, segment information is also included ineach transmission data packet.

Across the PDN, on the RA side, the RA first assembles the distributiondata packet from multiple transmission data packets. It then retrievesthe subframe number information in the distribution data packet header.Since the RA shares the same common subframe number with the BS, itforwards the N byte data payload to the BS at the correspondent videosubframe. FIG. 13 illustrates this process.

In another embodiment, instead of assembling the incoming video packets,the DA adds the necessary information to an individual video packet, asit arrives at the DA, and then sends it out as a distribution datapacket. Since multiple video packets can fit into one video subframe,the DA needs to indicate their sequential order to the RA. Therefore,the distribution data packet header must contain the common subframenumber and the packet sequence number. If one video subframe cantransmit maximum 16 video packets, then 4 bits are needed in the headerto identify the sequence number. In addition, the DA also includes onebit in the header to indicate the last distribution data packet to betransmitted in the subframe.

When the RA receives the distribution data packet, it sorts the databased on the subframe number and the packet sequence. If the lastdistribution data packet of the video subframe is received, it assemblesthem into N bytes payload for the video subframe and pads the unfilledbytes with a predefined byte pattern, such as 0x00. The RA then forwardsthe N bytes payload to the BS at the correspondent video subframe.

The subframe can be further divided into multiple video broadcast slots.In this case, the common subframe number does not have enough resolutionto identify the resource. If the slot configuration is known to both theCS and the BSs, the DA can provide the video slot number in thedistribution data packet header to identify it.

Furthermore, the video broadcast slot can be dynamically allocated bythe CS based on the properties of the video program. In this case, theslot can be identified by its construction subchannel numbers. The DAshould indicate these numbers to the RA as well. For efficiency reasons,the subchannel numbers may be expressed using compression format. In oneembodiment, all the subchannels in a video slot are consecutive. The DAonly indicates the start subchannel number and the total number ofsubchannels in the video slot. In another embodiment, the subchannelsare distributed. The DA uses bitmap to express their distributionpatterns.

For the described embodiments, the distributed frame numbersynchronization mechanism is at the core of the SFN operation. Themechanism sets up a synchronized mapping function between the time andthe common frame number. It can be developed based on the same timereference known to all the base stations and the CSs.

In one embodiment, the global positioning system (GPS) is used as thecommon time reference. A GPS receiver is integrated with each BS or CS.The GPS receiver generates a pulse periodically (e.g., every second).Since the AFS frame structure has a 2.5 ms subframe, every second 400subframes are transmitted. In order to establish a common subframenumber within the network, each BS or CS will track its own subframecounter in the following manner:

1. The counter is stored as an internal variable in the device memory.

2. For every subframe, the counter is incremented by 1.

3. At the time when the GPS pulse arrives, it is reset to 0.

Since the BSs and CSs are all synchronized by the GPS signal, theircounters remain aligned.

The maximum PDN transmission delay is also known to BSs and CSs. In oneembodiment, the value is measured during the pre-deployment networkdesign and is stored in CSs and BSs during its initial configuration.The quality of service mechanism in the PDN ensures that the actual PDNtransmission delay is always less than the maximum delay. However, ifthe maximum PDN transmission delay is changed when the PDNinfrastructure updates, the new latency value needs to be updated forall the CSs and BSs accordingly.

In another embodiment, the maximum value is transmitted together withthe distribution packet as part of the time synchronization information.In this way, each packet can have a different maximum delay value, whichprovides an update mechanism when the maximum PDN transmission delaychanges.

The following description provides specific details for a thoroughunderstanding of the various embodiments and for the enablement of oneskilled in the art. However, one skilled in the art will understand thatthe invention may be practiced without such details. In some instances,well-known structures and functions have not been shown or described indetail to avoid unnecessarily obscuring the description of theembodiments.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” Words using the singular or pluralnumber in this Detailed Description section also include the plural orsingular number respectively. Additionally, the words “herein,” “above,”“below” and words of similar import, when used in this application,shall refer to this application as a whole and not to any particularportions of this application. When the claims use the word “or” inreference to a list of two or more items, that word covers all of thefollowing interpretations of the word: any of the items in the list, allof the items in the list, and any combination of the items in the list.

The above detailed description of the embodiments of the invention isnot intended to be exhaustive or to limit the invention to the preciseform disclosed above or to the particular field of usage mentioned inthis disclosure. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. Also, the teachingsof the invention provided herein can be applied to other systems, notnecessarily the system described above. The elements and acts of thevarious embodiments described above can be combined to provide furtherembodiments.

All of the above patents and applications and other references,including any that may be listed in accompanying filing papers, areincorporated herein by reference. Aspects of the invention can bemodified, if necessary, to employ the systems, functions, and conceptsof the various references described above to provide yet furtherembodiments of the invention.

Changes can be made to the invention in light of the above “DetailedDescription.” While the above description details certain embodiments ofthe invention and describes the best mode contemplated, no matter howdetailed the above appears in text, the invention can be practiced inmany ways. Therefore, implementation details may vary considerably whilestill being encompassed by the invention disclosed herein. As notedabove, particular terminology used when describing certain features oraspects of the invention should not be taken to imply that theterminology is being redefined herein to be restricted to any specificcharacteristics, features, or aspects of the invention with which thatterminology is associated.

In general, the terms used in the following claims should not beconstrued to limit the invention to the specific embodiments disclosedin the specification, unless the above Detailed Description sectionexplicitly defines such terms. Accordingly, the actual scope of theinvention encompasses not only the disclosed embodiments, but also allequivalent ways of practicing or implementing the invention under theclaims.

While certain aspects of the invention are presented below in certainclaim forms, the inventors contemplate the various aspects of theinvention in any number of claim forms. Accordingly, the inventorsreserve the right to add additional claims after filing the applicationto pursue such additional claim forms for other aspects of theinvention.

We claim:
 1. A method for data communication by a control server connected via a packet data network (PDN) to a plurality of base stations in a plurality of cells, the plurality of base stations having synchronized timing of radio transmission frames and capable of transmitting data using a same time-frequency resource in a single frequency network (SFN), the method comprising: receiving broadcast data to be transmitted by the plurality of base stations; adding synchronization protocol headers to the broadcast data to form distribution data packets, the synchronization protocol headers providing information to the plurality of base stations to identify a radio transmission frame and enable transmission of the broadcast data using the same time-frequency resource in the SFN, each of the added synchronization protocol headers including: a packet sequence number enabling each of the plurality of base stations to restore a sequential order of its received distribution data packets; and a time synchronization parameter indicating a start time for the radio transmission frame; and distributing the distribution data packets via the PDN to the plurality of base stations for transmission of the broadcast data by the plurality of base stations.
 2. The method of claim 1, wherein a synchronization protocol header is inserted in the beginning, in the middle, or at the end of a data payload containing broadcast data.
 3. The method of claim 1, wherein the start time of the time synchronization is set at a time in the future that accounts for the maximum transmission delay in the PDN.
 4. The method of claim 1, wherein the time synchronization parameter is specified using a time unit related to a transmission time interval.
 5. The method of claim 4, wherein the transmission time interval is specified with respect to a radio transmission frame.
 6. The method of claim 5, wherein the transmission time interval is specified as a radio transmission subframe.
 7. The method of claim 5, wherein the radio transmission frame contains orthogonal frequency division multiplex (OFDM) signals.
 8. The method of claim 5, wherein a length of the radio transmission frame is 10 ms.
 9. The method of claim 1, wherein the time synchronization parameter is specified in a bit field in the synchronization protocol header.
 10. The method of claim 1, wherein the packet sequence number facilitates detection of the loss of a data packet at each of the plurality of base stations.
 11. The method of claim 1, wherein a value of the packet sequence number is specified in a bit field in the synchronization protocol header.
 12. The method of claim 11, wherein the bit field has a sufficient width to specify a maximum number of packets in a transmission period.
 13. The method of claim 1, wherein a cyclic redundancy check (CRC) or checksum field is added to each distribution data packet.
 14. The method of claim 1, wherein the data distribution network is either a wired network or a wireless network.
 15. A data distribution facility for distributing broadcast data via a packet data network (PDN) to a plurality of base stations in a plurality of cells, the plurality of base stations having synchronized timing of radio transmission frames and capable of transmitting data using a same time-frequency resource in a single frequency network (SFN), the data distributing facility comprising: an apparatus configured to receive broadcast data to be transmitted by the plurality of base stations; an apparatus configured to add synchronization protocol headers to the broadcast data to form distribution data packets, the synchronization protocol headers providing information to the plurality of base stations to identify a radio transmission frame and to transmit the broadcast data using the same time-frequency resource in the SFN, each of the added synchronization protocol headers including: a packet sequence number enabling each of the plurality of base stations to restore a sequential order of its received distribution data packets; and a time synchronization parameter indicating a start time for the radio transmission frame; and an apparatus configured to distribute the distribution data packets via the PDN to the plurality of base stations for transmission of the broadcast data by the plurality of base stations.
 16. In a multi-cell communication system, a method for data communication by a base station connected to a control server via a packet data network (PDN), the base station being one of a plurality of base stations serving a plurality of mobile stations in a plurality of cells, the method comprising: maintaining a synchronized timing of radio transmission frames with other base stations of the plurality of base stations by synchronizing to a reference common to the plurality of base stations; receiving data distribution packets from the control server, each data distribution packet containing a synchronization protocol header with a packet sequence number and a time synchronization parameter; decoding the packet sequence numbers and restoring the sequential order of the received distribution data packets based on the packet sequence numbers; decoding the time synchronization parameters and determining start times for radio transmission frames based on the time synchronization parameters; and transmitting broadcast data using the same time-frequency resource as other base stations in the plurality of base stations in a single frequency network (SFN).
 17. The method of claim 16, wherein a radio transmission frame comprises a plurality of subframes and each subframe contains multiple OFDM symbols.
 18. The method of claim 16, wherein a length of the radio transmission frame is 10 ms.
 19. The method of claim 16, wherein the reference is a global positioning system (GPS) time reference signal.
 20. The method of claim 16, further comprising buffering the received distribution data packet in an electronic memory.
 21. The method of claim 16, further comprising determining whether a distribution data packet has been lost or received incorrectly.
 22. The method of claim 21, wherein, when a distribution data packet has been lost or received incorrectly, an error protection mechanism is activated to avoid interfering with transmissions by other base stations in the plurality of base stations.
 23. The method of claim 22, wherein the error protection mechanism is to remain silent at least for the duration of a transmission period associated with the distribution data packet that has been lost or received incorrectly.
 24. A base station in a multi-cell communication system that consists of a plurality of base stations in a plurality of cells, the base station connected to a control server via a packet data network (PDN) and serving a plurality of mobile stations in a cell using a same time-frequency resource as other base stations in a single frequency network (SFN), the base station comprising: an apparatus configured to maintain a synchronized timing of radio transmission frames with the other base stations by synchronizing to a reference common to the plurality of base stations; a data receiving unit to receive data distribution packets from the control server, each data distribution packet containing a synchronization protocol header with a packet sequence number and a time synchronization parameter; an apparatus configured to decode the packet sequence numbers and restore the sequential order of the received distribution data packets based on the packet sequence numbers; an apparatus configured to decode the time synchronization parameters and determining start times for radio transmission frames based on the time synchronization parameters; and a transmitter configured to transmit broadcast data using a same time-frequency resource as other base stations in a single frequency network (SFN).
 25. In a multi-cell communication system, a method for data communication by a base station connected to a control server via a packet data network (PDN), the base station being one of a plurality of base stations serving a plurality of mobile stations in the plurality of cells, the plurality of base stations having synchronized timing of radio transmission frames and capable of transmitting data using a same time-frequency resource in a single frequency network (SFN), the method comprising: receiving a data distribution packet from the control server, wherein: the data distribution packet comprises a synchronization protocol header and broadcast data; and the synchronization header includes a packet sequence number and a time synchronization parameter; buffering the received distribution data packet in an electronic memory; recovering the packet sequence number and the time synchronization parameter from the received data distribution packet; restoring, if needed, a sequential order of the received data distribution packet as compared with other received data distribution packets based on its packet sequence number; deriving, based on the packet sequence number and the time synchronization parameter, a time for transmission of the broadcast data; scheduling the transmission of the broadcast data based on the derived time; and transmitting the broadcast data over the single frequency network (SFN) at the derived time. 